Streptococcal Infections (cont.)

Charles Patrick Davis, MD, PhD

Dr. Charles "Pat" Davis, MD, PhD, is a board certified Emergency Medicine doctor who currently practices as a consultant and staff member for hospitals. He has a PhD in Microbiology (UT at Austin), and the MD (Univ. Texas Medical Branch, Galveston). He is a Clinical Professor (retired) in the Division of Emergency Medicine, UT Health Science Center at San Antonio, and has been the Chief of Emergency Medicine at UT Medical Branch and at UTHSCSA with over 250 publications.

Mary D. Nettleman, MD, MS, MACP

Mary D. Nettleman, MD, MS, MACP is the Chair of the Department of Medicine at Michigan State University. She is a graduate of Vanderbilt Medical School, and completed her residency in Internal Medicine and a fellowship in Infectious Diseases at Indiana University.

Melissa Conrad Stöppler, MD

Melissa Conrad Stöppler, MD, is a U.S. board-certified Anatomic Pathologist with subspecialty training in the fields of Experimental and Molecular Pathology. Dr. Stöppler's educational background includes a BA with Highest Distinction from the University of Virginia and an MD from the University of North Carolina. She completed residency training in Anatomic Pathology at Georgetown University followed by subspecialty fellowship training in molecular diagnostics and experimental pathology.

What is group A Streptococcus (GAS)?

Group A Streptococcus is defined as a gram-positive bacterial genus composed of Streptococcus pyogenes strains. Group A Streptococcus strains have a similar surface antigen recognized by Lancefield serogrouping tests, termed the Lancefield group A antigen. Lancefield groups (there are about 18 Lancefield groups) are composed of different Streptococcus species groups that have specific antigens and are distinguished by specific Lancefield antibody tests. In addition, group A Streptococcus strains are beta hemolytic (beta hemolytic means the bacteria lyse red blood cells suspended in agar plates with secreted substances, see for example, Fig. 3). These tests are mentioned because they are frequently used to distinguish group A Streptococcus bacteria from group B, group C, and other Streptococcus groups. Group A Streptococcus bacteria appear as pairs and chains when gram-stained (see Fig. 1); these bacteria are also termed "beta strep, GAS, and GABHS." Although these bacteria can harmlessly colonize people on their throat and skin, sometimes they can cause mild to serious diseases. GAS bacteria have been causing diseases in humans probably since humans first developed.

Streptococcus pyogenes (GAS) bacteria have many components that contribute to the pathogen's ability to cause disease:

Lipoteichoic acid on its surface helps the GAS bacteria to bind to epithelial cell membranes.

Exotoxins cause the scarlet fever rash, damage organs, may cause shock, and inhibit the human immune system, while the human immune system stimulators may stimulate the immune system to produce antibodies that likely play a role in the development of autoimmune responses that can lead to glomerulonephritis or acute rheumatic fever. S. pyogenes (GAS) has over 100 serotypes that may vary somewhat in their ability to produce the above components that contribute to the pathogenicity of each strain of the bacteria.